Certification Problem

Input (TPDB SRS_Standard/Waldmann_19/random-78)

The rewrite relation of the following TRS is considered.

a(b(a(b(x1)))) → b(b(a(b(x1)))) (1)
b(b(a(a(x1)))) → a(b(a(a(x1)))) (2)
a(a(b(b(x1)))) → b(a(a(b(x1)))) (3)

Property / Task

Prove or disprove termination.

Answer / Result

Yes.

Proof (by AProVE @ termCOMP 2023)

1 String Reversal

Since only unary symbols occur, one can reverse all terms and obtains the TRS
b(a(b(a(x1)))) → b(a(b(b(x1)))) (4)
a(a(b(b(x1)))) → a(a(b(a(x1)))) (5)
b(b(a(a(x1)))) → b(a(a(b(x1)))) (6)

1.1 Semantic Labeling

Root-labeling is applied.

We obtain the labeled TRS
ba(ab(ba(ab(x1)))) → ba(ab(bb(bb(x1)))) (7)
ba(ab(ba(aa(x1)))) → ba(ab(bb(ba(x1)))) (8)
aa(ab(bb(bb(x1)))) → aa(ab(ba(ab(x1)))) (9)
aa(ab(bb(ba(x1)))) → aa(ab(ba(aa(x1)))) (10)
bb(ba(aa(ab(x1)))) → ba(aa(ab(bb(x1)))) (11)
bb(ba(aa(aa(x1)))) → ba(aa(ab(ba(x1)))) (12)

1.1.1 Dependency Pair Transformation

The following set of initial dependency pairs has been identified.
ba#(ab(ba(ab(x1)))) → ba#(ab(bb(bb(x1)))) (13)
ba#(ab(ba(ab(x1)))) → bb#(bb(x1)) (14)
ba#(ab(ba(ab(x1)))) → bb#(x1) (15)
ba#(ab(ba(aa(x1)))) → ba#(ab(bb(ba(x1)))) (16)
ba#(ab(ba(aa(x1)))) → bb#(ba(x1)) (17)
ba#(ab(ba(aa(x1)))) → ba#(x1) (18)
aa#(ab(bb(bb(x1)))) → aa#(ab(ba(ab(x1)))) (19)
aa#(ab(bb(bb(x1)))) → ba#(ab(x1)) (20)
aa#(ab(bb(ba(x1)))) → aa#(ab(ba(aa(x1)))) (21)
aa#(ab(bb(ba(x1)))) → ba#(aa(x1)) (22)
aa#(ab(bb(ba(x1)))) → aa#(x1) (23)
bb#(ba(aa(ab(x1)))) → ba#(aa(ab(bb(x1)))) (24)
bb#(ba(aa(ab(x1)))) → aa#(ab(bb(x1))) (25)
bb#(ba(aa(ab(x1)))) → bb#(x1) (26)
bb#(ba(aa(aa(x1)))) → ba#(aa(ab(ba(x1)))) (27)
bb#(ba(aa(aa(x1)))) → aa#(ab(ba(x1))) (28)
bb#(ba(aa(aa(x1)))) → ba#(x1) (29)

1.1.1.1 Dependency Graph Processor

The dependency pairs are split into 1 component.